Exceeding Oil and Mercury Standards
Question: Recently we learned that our plant effluent is well above the city standards for oil and mercury.
Recently we learned that our plant effluent is well above the city standards for oil and mercury. The maximum permitted oil is 250 parts per million, and the maximum for mercury is 0.5 parts per billion. Our plant operations include machining, washing and mass finishing. We machine with soluble oil and have that hauled away when it needs to be changed. Our oil level is still more than 600 parts per million, and the mercury level is more than five times the limit. Where does all this oil and mercury come from? S.M.
It comes from the compounds you use, the machining oil, the tramp oils and from the janitorial cleaning compounds. An informal survey of manufacturers of mass-finishing compounds, coolants and cleaning products revealed to us that almost all of them think they meet the mercury requirement, yet few of them have had their products tested and few actually pass the requirement. Surprisingly, many also think they meet the FOG (Fats, Oils and Greases) requirement. The reason is that the government considers animal and vegetable oils just as offensive as petroleum oils. It is a challenge to formulate products while avoiding the offending raw ingredients. A lot of mercury gets into compounds from alkaline sources, and these are found in the cleaners and the coolants. The FOG come not only from the obvious petroleum oils used in soluble oil coolants, straight machining oil, hydraulic oil but also from animal and vegetable oils used to manufacture cleaners, lubricants and rust inhibitors. The government regulations impose difficult limits on how these materials are used to make cost effective industrial and janitorial compounds.
Some fluid manufacturers have developed products to meet these stringent requirements. I suggest that you analyze all the fluids you purchase for metalworking. Test anything that can end up in the plant effluent, including janitorial compounds, hydraulic oils or other oils. The test for FOG is Method 5520B, from Standard Methods for the Examination of Water and Wastewater. The test for mercury is Method 245.1, from USEPA Document 600/4-79-020. The lab that tested your wastewater should be able to test the pure fluids. Do your lab a favor and suggest that they dilute the concentrates to a 10% solution, because some compounds at full strength can compromise the test equipment. From the content at 10%, you can calculate the mercury and FOG levels of the use concentration. Even if you have not been challenged by governmental authorities, it is good to know how much FOG and mercury is in any product you send down the drain. On a practical note, we have found that companies using soluble or stamping oils (as opposed to straight oils) will meet the discharge standards on FOG. Frequently, those companies wash after machining, and they have the used wash water hauled along with the used coolant. The mass finishing following the wash can be flowed through and meet both FOG and mercury tests. That assumes, of course, that all the fluids coming in contact with the parts will have low mercury and FOG levels. Sometimes, a change to synthetic coolants or stamping fluids can eliminate the washing step prior to mass finishing.